This invention relates to a method and apparatus for continuously producing resin films and also to an installation therefor.
Hitherto, resin films have been produced by casting a resin solution in film form over a casting drum through extrusion or coating, or casting the resin solution likewise over an endless belt in order to allow it to set and become hardened, then blowing hot air onto the film-form cast resin to allow the cast resin to become hardened to a self-supportable level, and subsequently separating the film-form resin from the casting drum or endless belt.
However, when hot air as blown in a jet stream through a nozzle or the like is applied to the surface of the film-form resin solution cast over the endless belt or the like surface, the surface of the resin film is often subject to the trouble of wind ripples being formed thereon under the force of the hot air, even if the resin solution is of high viscosity of, for example, 100 to 1000 poise. Another problem is that when hot air is blown through a nozzle onto the resin film cast over the endless belt, the cast resin film is subject to temperature irregularity in the transverse direction thereof because of the endless belt is continuously moving, with the result that no uniformity can be obtained in setting and hardening speed, surface irregularity being thus caused to the resin film. Such wind ripples and surface irregularity due to temperature unevenness will pose no problem in case where the resin film is used for foodstuff wrapping or the like purposes, but where it is used with electronic parts and the like, it will affect the electromagnetic characteristics of those parts.
The pulleys over which the endless belt is trained are heated by the hot air blown for setting and hardening the cast resin and accordingly the temperature of the endless belt itself is high because of heat transfer from the heated pulleys. Therefore, when a resin solution of, for example, the reactive setting type is cast in film form, setting and drying will occur with the film form resin simultaneously in parallel and randomly. This has made it difficult to control both the setting reaction speed and drying speed of the resin.